Peel potatoes and cut into fries.
Soak fries in cold water for 30 minutes.
Heat oil in deep pan to 325°F.
Fry potatoes for 5 minutes until slightly soft.
Remove fries and set on paper towels.
Mix flour, baking powder, and salt in bowl.
Whisk in sparkling water until batter forms.
Pat cod fillets dry with paper towels.
Dip cod fillets in batter until fully coated.
Heat oil to 350°F for fish frying.
Fry cod until golden, about 6 minutes.
Remove and place fish on paper towels.
Increase oil heat to 375°F for fries.
Fry potatoes again until golden and crispy.
Serve fish and fries with lemon wedges.